1. Field of the Invention
The present invention relates to mortise locks equipped with lever handles. More particularly, the present invention relates to mortise locks where inner and outer lever handles are held level by a common spring return mechanism and where it is necessary to support one handle in the level position while the opposite handle is being operated against the pressure of the common spring return.
2. Description of Related Art
A mortise lock is operated by inner and outer handles located on opposite sides of the mortise lock case and typically includes a spring return mechanism that returns a handle to its initial position after it is rotated. Provided the mortise lock is in the unlocked state, rotation of either handle will retract the latch bolt, compress the spring return and open the door. When the rotated handle is released, the spring return mechanism returns the handle to its original position.
In a conventional mortise lock design, the inner and outer handles are mounted on separate shafts and operate independently, thereby allowing one handle to be locked while still permitting the opposite handle to turn and open the door. Because both handles ultimately connect to the latchbolt, however, a single spring return mechanism is often used to return both handles to their starting level position.
When the handles are conventional round doorknobs, rotation of one knob and compression of the common spring return mechanism due to that rotation will normally have no effect on the opposite knob. However, when lever handles are used, compression of the common spring return mechanism, by rotation of one lever handle, causes the opposite lever handle to droop. This droop occurs because, unlike a cylindrically symmetrical doorknob, the center of gravity of a lever handle is offset from its axis of rotation. This offset constantly applies a gravitational torque to the lever handle due to the weight of the lever portion of the handle, which must be opposed by the spring return mechanism. When the counteracting spring pressure is removed the unused lever handle droops downward, following the motion of the lever handle in use.
The appearance of a drooping handle is visually undesirable. Moreover, in some applications this drooping motion of the unused handle interferes with the desired function of the lock. One such application is in a monitored mortise lock design in which separate switches are operated by the handles. The switches are triggered whenever the handle they monitor rotates. This is intended to allow the monitoring system to determine which handle was used.
When a switch-monitored mortise lock of this type has conventional round doorknobs installed, the switches operate independently and the monitoring system is able to determine which of the two handles was operated to open the mortise lock. Thus, the monitoring system can tell whether the door was opened from the inside or from the outside.
However, when lever handles are installed in a switch-monitored mortise lock of this type, the drooping motion of the unused lever handle causes both switches to operate when either handle is used. This prevents the monitoring system from detecting which handle was used to open the door. The problem also occasionally occurs with round doorknobs in mortise lock designs that frictionally transmit some of the rotational force from the operated handle to the non-operated handle.
Although a redesign of the mortise lock mechanism to incorporate additional springs in the mortise case may solve this problem, such redesign is expensive and is not warranted for the limited number of applications where handle droop during operation of the opposite handle is a problem.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a handle support mechanism that will prevent the non-operated handle from turning when the opposite handle is being rotated.
It is another object of the present invention to provide a handle support mechanism that can be installed on existing designs in the field without modification to the mortise lock.
A further object of the invention is to provide a handle support mechanism that is relatively inexpensive to manufacture.
The above and other objects, which will be apparent to those skilled in art, are achieved in the present invention which is directed to a handle support mechanism for attachment to a lock having first and second handles. The mechanism includes first and second friction elements with corresponding friction surfaces. The friction elements are connected to and rotationally driven by their respective handles when the handles are turned. First and second non-rotatable friction surfaces are non-rotatably mounted relative to the lock such that they are in frictional contact with the corresponding friction surfaces on the friction elements. A bracket may be free-floating or mounted to the lock and acts to hold the friction surfaces on the first and second friction elements in frictional contact with the first and second non-rotatable friction surfaces. Engagement between the friction surfaces on the friction elements (which turn with the handles) and the non-rotatable friction surfaces (which cannot turn with the handles) prevents an unsupported handle from rotating or drooping.
The bracket is preferably a spring bracket that applies an inward spring force to engage the rotating and non-rotating friction surfaces. The friction elements may be formed as discs with cylindrical bearing surfaces that engage bearing holes in the bracket. The handle support mechanism is particularly suitable for installation to the exterior of a mortise lock. The preferred embodiment may be installed with no fasteners without modifying the mortise lock in any way. In this design the bracket is a generally U-shaped spring bracket that includes a base portion and a pair of legs separated by a distance corresponding to the thickness of the mortise lock. The legs of the bracket extend to opposite sides of the mortise lock and the bracket floats, automatically moving towards a handle that is turned to reduce friction on that side and increase friction on the opposite, non-turning side.
Although the friction surfaces may provide a uniform friction as the handles turn, in the preferred embodiment of the invention, the rotating and non-rotating friction surfaces use dimples and notches to releasably engage each other. This provides a xe2x80x9cdetentxe2x80x9d action that initially resists handle rotation with a relatively high friction, but then drops to a relatively low friction level as the handle turns from its initial position. In the embodiment illustrated, four dimples are produced on each inner, friction surface, leg of the spring bracket and four corresponding notches are produced around the perimeter of each friction disc.
The bracket is preferably made of spring steel and the friction discs are preferably formed of sintered powdered metal. The sintered metal part is infiltration treated to increase density and reduce porosity, then plated, and finally an anti-wear coating applied. The anti-wear coating may include polytetrafluoroethylene (PTFE), which paradoxically reduces friction on the friction surfaces of the friction discs. This has the desirable effect (due to the dimple/notch detent interaction) that the desired handle support action is produced in the vicinity of the initial handle position and low handle turning friction is produced elsewhere.